Successful fish oil sparing in White Seabass feeds using saturated fatty acid-rich soybean oil and 22:6n-3 (DHA) supplementation

Abstract

Like other carnivorous species, White Seabass typically demand a nutrient-dense feed. Research is ongoing to develop formulations that contain minimal amounts of marine-origin protein and lipid, i.e., fish meal and fish oil, as a mean of reducing production costs and pressure on reduction fisheries. Previous research has shown that a greater level of fish oil-sparing is possible with saturated fatty acid-rich, hydrogenated soybean oil than with C18 polyunsaturated fatty acid-rich standard soybean oil. To confirm this observation and to assess whether docosahexaenoic acid (DHA) is a limiting factor in fish oil sparing with soy-derived lipids, we evaluated the performance and tissue fatty composition of juvenile White Seabass fed diets containing fish oil, or standard or hydrogenated soybean oil with or without the addition of an algal DHA supplement. In addition, a low temperature stress challenge was done after the feeding trial. Fish fed the hydrogenated soybean oil feeds exhibited growth performance equivalent to those fed the fish oil feed, regardless of DHA supplementation. Growth performance was impaired among fish fed the standard soybean oil feed compared to those fed the fish oil control feed, but the addition of DHA corrected this effect. Dietary treatments significantly affected fatty acid composition of fillet, liver, eye, and brain tissues. In terms of long-chain polyunsaturated fatty acids and n-3 fatty acids, the tissues of fish fed the hydrogenated soybean oil feeds were equivalent to those of fish fed the fish oil feed. Tissues of fish fed the standard soybean oil feeds exhibited significantly lower levels of these beneficial fatty acids; however, this effect was corrected by dietary DHA supplementation. The low temperature stress challenge induced elevated plasma cortisol, and reduced glucose, osmolality and hematocrit; though dietary inclusion of soybean oils did not appear to negatively affect stress tolerance. Results suggest that fish oil sparing in White Seabass feeds is limited by DHA, and that DHA bioavailability may be greater in the presence of hydrogenated soybean oil than standard soybean oil.